kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/fs/adfs/dir_fplus.h b/fs/adfs/dir_fplus.h
new file mode 100644
index 000000000..d729b1591
--- /dev/null
+++ b/fs/adfs/dir_fplus.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/fs/adfs/dir_fplus.h
+ *
+ *  Copyright (C) 1999 Russell King
+ *
+ *  Structures of directories on the F+ format disk
+ */
+
+#define ADFS_FPLUS_NAME_LEN	255
+
+#define BIGDIRSTARTNAME ('S' | 'B' << 8 | 'P' << 16 | 'r' << 24)
+#define BIGDIRENDNAME	('o' | 'v' << 8 | 'e' << 16 | 'n' << 24)
+
+struct adfs_bigdirheader {
+	__u8	startmasseq;
+	__u8	bigdirversion[3];
+	__le32	bigdirstartname;
+	__le32	bigdirnamelen;
+	__le32	bigdirsize;
+	__le32	bigdirentries;
+	__le32	bigdirnamesize;
+	__le32	bigdirparent;
+	char	bigdirname[1];
+} __attribute__((packed, aligned(4)));
+
+struct adfs_bigdirentry {
+	__le32	bigdirload;
+	__le32	bigdirexec;
+	__le32	bigdirlen;
+	__le32	bigdirindaddr;
+	__le32	bigdirattr;
+	__le32	bigdirobnamelen;
+	__le32	bigdirobnameptr;
+} __attribute__((packed, aligned(4)));
+
+struct adfs_bigdirtail {
+	__le32	bigdirendname;
+	__u8	bigdirendmasseq;
+	__u8	reserved[2];
+	__u8	bigdircheckbyte;
+} __attribute__((packed, aligned(4)));